"Regarding the GPS - I don't think it has the resolution or refresh rate to be able to provide valuable feedback to the algorithm."
The point about GPS is that the system should be aware of where it's going (i.e. map following as one input), and that there's no need to follow the other car that exited towards the right.
The raw GPS data is supposed to be combined with other inputs, such as previous curves and wheel speed sensors, to create a more-trustworthy fix than GPS alone. The usual Kalman filtering, etc.
For comprison: I've seen videos that indicate that some Bentley cars will downshift for an upcoming curve, based on a GPS-aided location (and a map of course) view of the path ahead. Also, some Mercedes will provide predictive illumination into (for example) the correct side for an upcoming roundabout, again using GPS combined with some dead reckoning.
Even my (fairly old) 2008 Mercedes correctly deduced my lane choice, going left or right at a split, in a tunnel under a harbour somewhere (i.e. no GPS signal). Apparently the GPS chip itself (probably uBlox) includes inputs for left and right wheel speed sensors, to detect not just motion, but the wheel speed differences implying direction choices. And the GPS chip itself provides the dead reckoning, built in. So I've read.
The Tesla appears to be blissfully unaware of where it is, and where it's going - at least in the immediate short term for planning the next curve. Presumably it has enough map-smart to know how to get where it's going. Supposedly it'll open your garage door for you as you arrive.
The best we can say is that they're not finished yet.